This application claims the benefit of Korean Patent Application No. 2001-45799, filed on Jul. 30, 2001, which is hereby incorporated by reference for all purposes as if fully set forth herein.
1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly to a transflective LCD device including a poly crystalline silicon (p-Si) thin film transistor (TFT).
2. Discussion of the Related Art
In general, transflective LCD devices function as both transmissive and reflective LCD devices at the same time. The transflective LCD devices can use light of a backlight and ambient light of natural or artificial light source and thus do not depend on environmental conditions. Therefore, power consumption of the transflective LCD device is reduced. Accordingly, the transflective LCD devices are currently the subject of research and development.
FIG. 1 is a schematic plan view of an array substrate for a conventional transmissive LCD device.
In FIG. 1, a gate line 6, a storage line 7 and a data line 10 are formed on an array substrate 2. The gate line 6 includes a gate pad 4 at its one end. The storage line 7 is parallel to the gate line 6. The data line 10 including a data pad 8 at its one end crosses the gate line 6 and the storage line 7. The data line 10 defines a pixel region xe2x80x9cPxe2x80x9d with the gate line 6. A transparent pixel electrode 18 is formed at the pixel region xe2x80x9cPxe2x80x9d. A signal is applied to a gate pad terminal 5 contacting the gate pad 4 through a gate pad contact hole 32 and a data pad terminal 9 contacting the data pad 8 through a data pad contact hole 34 from exterior. A thin film transistor (TFT) xe2x80x9cTxe2x80x9d having a gate electrode 12, an active layer 17, and source and drain electrodes 14 and 16 is formed near a crossing point of the gate and data lines 6 and 10. The TFT xe2x80x9cTxe2x80x9d has a coplanar structure in which source and drain regions are formed in the same plane as the active layer 17. The active layer 17 is made of poly crystalline silicon. The pixel electrode 18 is connected to the drain electrode 16 through a drain contact hole 28. The gate electrode 12 and the source electrode 14 are connected to the gate line 6 and the data line 10, respectively. A storage capacitor xe2x80x9cCxe2x80x9d including the storage line 7 is formed at a portion of the pixel region xe2x80x9cPxe2x80x9d. The storage capacitor xe2x80x9cCxe2x80x9d also includes a metal layer 15 of island shape connected to the pixel electrode 18 through a storage contact hole 30. Charges are thereby stored in the storage line 7 and the metal layer 15.
FIG. 2 is a schematic cross-sectional view taken along a line IIxe2x80x94II of FIG. 1.
In FIG. 2, a buffer layer 20, namely, a first insulating layer is formed on a substrate 2 and a semiconductor layer 17 of island shape is formed on the buffer layer 20. A center portion of the semiconductor layer 17 is a first active region 17a functioning as an active channel, and edge regions of the semiconductor layer 17 are second active regions 17b and 17c doped with impurities a subsequent process. Next, a gate insulating layer 22, namely, a second insulating layer is formed on the semiconductor layer 17. Next, a gate electrode 12, a gate line 6 and a gate pad 4 of conductive metallic material are formed on the gate insulating layer 22. The gate line 6 extends along a first direction and is connected to the gate electrode 12 formed over the semiconductor layer 17. The gate pad 4 is disposed at one end of the gate line 6. A storage line 7 extends along the first direction and is parallel to the gate line 6. The second active regions 17b and 17c are doped with impurities by using the gate electrode 12 as a doping mask. After forming an interlayer insulator 24, namely, a third insulating layer on an entire surface of the substrate 2, the second active regions 17b and 17c are exposed by patterning the interlayer insulating layer 24 and the gate insulating layer 22. Next, a source electrode 14, a drain electrode 16, a storage electrode 15, a data line 10 and a data pad 8 are formed through depositing and patterning conductive metallic material. The source and drain electrodes 14 and 16 are connected to the second active regions 17b and 17c. The data pad 8 is disposed at one end of the data line 10 extending along a second direction and connected to the source electrode 14. Next, a passivation layer 26, namely, a fourth insulating layer having a drain contact hole 28, a storage contact hole 30, a gate pad contact hole 28 and a data pad contact hole 34 is formed through depositing and patterning transparent organic material. The drain electrode 16, the storage electrode 15, the gate pad 4 and the data pad 8 are exposed through the drain contact hole 28, the storage contact hole 30, the gate pad contact hole 28 and the data pad contact hole 34, respectively. Next, a pixel electrode 18 contacting the drain electrode 16, a gate pad terminal 5 contacting the gate pad 4 and a data pad terminal 9 contacting the data pad 8 are formed on the passivation layer 26 through depositing and patterning transparent conductive material.
The conventional transmissive LCD devices, however, have high power consumption due to a limitation of the light source. To overcome this problem, transflective LCD devices have been developed.
FIG. 3 is a schematic cross-sectional view of an array substrate for a conventional transflective LCD device.
In FIG. 3, an array substrate 30 for a transflective LCD device has substantially same structure as that for a transmissive LCD device except a pixel electrode 63 and a reflective electrode 72 at a pixel region xe2x80x9cPxe2x80x9d. That is, a gate line 41 and a data line 54 of matrix type are formed on the substrate 30, and a TFT xe2x80x9cTxe2x80x9d is formed near a crossing point of the gate and data lines 41 and 54. The TFT xe2x80x9cTxe2x80x9d of coplanar structure is a p-Si TFT having an active layer made of poly crystalline silicon. Gate and data pads 44 and 56 to which a signal is applied are formed at one end of the gate and data lines 41 and 54, respectively. Further, gate and data pad terminals 64 and 66 of transparent conductive material are connected to the gate and data pads 44 and 56, respectively. The TFT xe2x80x9cTxe2x80x9d includes an active layer 36, a gate electrode 40, source and drain electrodes 50 and 52. The active layer 36 includes an active extension portion 37 at the pixel region xe2x80x9cPxe2x80x9d. A storage line 42 of the same material as the gate line 41 is formed along a first direction and crosses the pixel region xe2x80x9cPxe2x80x9d. Further, the storage line 42 includes a storage electrode 43 at the pixel region xe2x80x9cPxe2x80x9d. A transparent pixel electrode 63 is connected to the drain electrode 52 through a first drain contact hole 62. A reflective electrode 72 connected to the pixel electrode 63 through a second drain contact hole 70 is formed over the storage electrode 43.
Therefore, a storage capacitor portion xe2x80x9cCxe2x80x9d and a reflective portion xe2x80x9cExe2x80x9d are formed at the same portion of the pixel region xe2x80x9cPxe2x80x9d. Here, the storage capacitor portion xe2x80x9cCxe2x80x9d includes a first storage capacitor between the active extension portion 37 and the storage electrode 43, and a second storage capacitor between the storage electrode 43 and the pixel electrode 63. Since the reflective electrode 72 covers the storage electrode 43, the reflective portion xe2x80x9cExe2x80x9d also covers the storage capacitor portion xe2x80x9cCxe2x80x9d. The other portion of the pixel region xe2x80x9cPxe2x80x9d not including the reflective portion xe2x80x9cExe2x80x9d is a transmissive portion xe2x80x9cFxe2x80x9d.
In the array substrate for the conventional transflective LCD device, the reflective electrode is formed over the pixel electrode with an insulating layer interposed therebetween and connected to the pixel electrode through the second drain contact hole. As a result, the fabricating process has many steps and the production cost is high.
Accordingly, the present invention is directed to a liquid crystal display device that substantially obviates one or more of problems due to limitations and disadvantages of the related art.
An advantage of the present invention is to provide an array substrate including a reflective plate at a boundary of a pixel region under a transparent electrode, thereby simplifying fabrication steps, increasing production yield and display quality.
Additional features and advantages of the invention will be set forth in the description that follows, and in part will be apparent from the description, or may be learned by practice of the invention. Other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, an array substrate for a transflective liquid crystal display device includes a substrate; a thin film transistor on the substrate, the thin film transistor including an active layer, a gate electrode, a source electrode and a drain electrode; a gate line connected to the gate electrode; a data line connected to the source electrode, the data line defining a pixel region with the gate line; an active extension portion extending from the active layer to the pixel region; a first insulating layer on the active extension portion; a storage electrode on the first insulating layer over the active extension portion; a second insulating layer on the storage electrode; a reflective plate on the second insulating layer over the storage electrode, the reflective plate extending over one end of the data line and connected to an adjacent reflective plate; a third insulating layer on the reflective plate; and a pixel electrode on the third insulating layer, the pixel electrode extending over one end of the data line and connected to the drain electrode.
In another aspect, a fabricating method of an array substrate for a transflective liquid crystal display device includes forming a thin film transistor on a substrate, the thin film transistor including an active layer, a gate electrode, a source electrode and a drain electrode; forming a gate line connected to the gate electrode; forming a data line connected to the source electrode, the data line defining a pixel region with the gate line; forming an active extension portion extending from the active layer to the pixel region; forming a first insulating layer on the active extension portion; forming a storage electrode on the first insulating layer over the active extension portion; forming a second insulating layer on the storage electrode; forming a reflective plate on the second insulating layer over the storage electrode, the reflective plate extending over one end of the data line and connected to an adjacent reflective plate; forming a third insulating layer on the reflective plate; and forming a pixel electrode on the third insulating layer, the pixel electrode being extending over one end of the data line and connected to the drain electrode.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.